The Summoning Charm (Accio) was a charm that summoned an object toward the caster. It was able to summon objects in direct line of sight of the caster, as well as things out of view, by calling the object aloud after the incantation (unless the spell was cast nonverbally).

Being familiar with the object, and knowing where the object is all may play a part in this. However, there is no definite defined range for Accio. Anything can be pulled in from anywhere if the wielder had that power. Wizards and witches do have limits to their power, so that does not make it an unlimited range.

Accio, is only known to work on inanimate objects. While people, animals and magical creatures may be indirectly affected or moved by the charm, it can not move people directly through the charm it's self. Preforming an Accio charm on an object that an individual is holding or wearing carries significant risks.

just press once and once more to deactivate. Physics will cause things to keep moving after you deactivate the thing. Things that are in motion stay in motion till an opposite force applies onto it.